Timber structural members play an important part in the construction of building structures. Timber is commonly used for joists, beams, columns, rafters and frames because of its strengths for load bearing and its natural ability to withstand a variety of forces. Additionally, compared to metal based materials, timber structural members often cost less to manufacture and are more easily cut and processed for specific building requirements. A strong and useful type of structural member is an “I-joist”. The I-joist comprises two flange members with an interconnecting web member, resembling a letter “I” in its cross-section. I-joists have good load bearing and distribution capabilities and are key components in building construction.
The flanges of timber I-joists (hereon called “timber joists”) have historically been made from solid wood lumber or laminated timber. In order to obtain flanges of appropriate length and cross-sectional dimensions, relatively large diameter lumber is required. Any imperfection in the flange can greatly compromise the strength of the flange, so relatively high quality lumber is required for the manufacture of timber joists. This has led in turn to increased cost in production as well as raising natural resource conservation issues. Depending on the part of the log it is sawn from, the solid lumber may have issues with natural defects such as splinters, rot, abnormal growth and grain structures. Additionally, when sawn and prepared for commercial use the lumbers are prone to processing defects such as chipping, torn grain and timber wanes.
To address the problems associated with solid wood lumber, alternative forms of wood material for making timber joists have been sought. These include engineered wood composites such as plywood, laminated veneer lumber (“LVL”), oriented strand lumber (“OSL”) and oriented strand board (“OSB”). Wood composites have the advantage of being less expensive in raw material cost (as they are able to be formed from lower grade wood or even wood wastes) and do not have the problems associated with solid lumber defects. However, the energy and resource requirements in their manufacture are generally significantly higher as processed structural timber requires significantly more cutting, bonding, and curing than naturally formed timber. Also, timber joists made from wood composites do not have effective end grain connection and when used in building construction they are usually joined by bearing onto another member and nailed to deter sideway twisting and/or movement. This type of connection often requires further mounted metal braces which become design hindrances. Additionally, the metal braces are prone to oxidation and collapse in fire as the metal heats more readily than the timber, resulting in charring of the adjoining timber and loss of support.
United States Patent Application Publication 2011/0016824 describes a timber joist comprising first and second flanges connected together by a web, the web being structurally integral with the flanges. Both flanges comprise timber poles. While this joist is useful, it has been found that under high loads longitudinal splits or cracks may form in the timber. The splits or cracks are found to occur in regions of the timber about the web, and can lead to catastrophic failure of the joist under high load conditions.
It is an aspect of the present invention to provide a timber structural member that has an improved resistance to splitting or cracking for a given load. It is another aspect to provide an alternative to a timber structural member of the prior art.
The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.